The present disclosure relates generally to the treatment of cardiac tissue of a patient with ablative energy. More particularly, it relates to ablation of cardiac tissue using high voltage ablation, for example via high voltage electroporation ablation or irreversible electroporation (IEP) ablation.
There are many medical treatments that involve instances of cutting, ablating, coagulating, destroying, or otherwise changing the physiological properties of tissue. These techniques can be used beneficially to change the electrophysiological properties of tissue, for example by ablation of cardiac tissue to cure various cardiac conditions. As a point of reference, normal sinus rhythm of the heart begins with the sinoatrial node (or “SA node”) generating a depolarization wave front. The impulse causes adjacent myocardial tissue cells in the atria to depolarize, which in turn causes adjacent myocardial tissue cells to depolarize. The depolarization propagates across the atria, causing the atria to contract and empty blood from the atria into the ventricles. The impulse is next delivered via the atrioventricular node (or “AV node”) and the bundle of HIS (or “HIS bundle”) to myocardial tissue cells of the ventricles. The depolarization of cells propagates across the ventricles, causing the ventricles to contract. This conduction system results in the described, organized sequence of myocardial contraction leading to a normal heartbeat.
Sometimes, aberrant conductive pathways develop in heart tissue, which disrupts the normal path of depolarization events. For example, anatomical obstacles in the atria or ventricles can disrupt the normal propagation of electrical impulses. These anatomical obstacles (called “conduction blocks”) can cause the electrical impulse to degenerate into several circular wavelets that circulate about the obstacles. These wavelets, called “reentry circuits,” disrupt the normal activation of the atria or ventricles. Additionally, it has been hypothesized that multiple microeentrant wavelets can occur in myocardium that has remodeled, such that it can more easily sustain fibrillatory conduction patterns such as in atrial fibrillation. In such atrial myocardium, there may be a dispersion of atrial refractoriness, whereby there is variation in the effective refractory period over the atrial wall. When such tissue is exposed to rapid conduction wavefronts or asynchronus ectopic focal triggers, a portion of those myocardial cells are still in a refractory state. This leads to the circulating chaotic wavefronts that are known collectively as atrial fibrillation (AF). Curative ablation therapies for AF focus on creation of linear lesions that compartmentalize the atria and direct conduction along selected pathways that are intended to promote organized conduction while isolating AF triggers from connecting with the atria.
The aberrant conductive pathways create abnormal, irregular, and sometimes life-threatening heart rhythms called arrhythmias. An arrhythmia can take place in the atria, for example, as in atrial tachycardia, atrial fibrillation, or atrial flutter. The arrhythmia can also take place in the ventricle, for example, as in ventricular tachycardia.
As indicated above, surgical procedures can be performed to treat heart arrhythmias, and in particular via formation of one or more lesions that interrupt the conduction routes of the most common reentry circuits. For example, a surgical procedure called the “Maze” procedure (and variations of the Maze procedure) was designed to eliminate atrial fibrillation permanently. The procedure employs incisions in the right and left atria which divide the atria into electrically isolated portions that in turn results in an orderly passage of the depolarization wave front from the SA node to the AV node while preventing reentrant wave front propagation.
The lesions formed in connection with the Maze procedure, as well as other cardiac tissue applications, can be imparted via ablation. Conventionally, cardiac tissue ablation is effectuated by placement of one or more ablating members (e.g., electrodes), and applying energy at certain levels to achieve the desired result of killing of cells at the ablation site while leaving the basic structure of the organ to be ablated in tact. RF energy has been found to be highly viable in this regard, and is commonly employed. Other ablative techniques include ultrasound, microwave, laser, cytotoxic agents, etc. In certain instances, conventional cardiac tissue ablation systems may not achieve optimal results in terms of complete transmural ablation (e.g., ablation lesion extending through a thickness of the ablated tissue structure) with minimal, if any, impact on surrounding tissue. For example, excessive thermal conditions may be a concern with RF ablation. Thus, any improvements in cardiac tissue ablation systems and methods that limit hyperthermy will be well-received.